The present invention relates to a process for the preparation of 2-chloropyridine by chlorination of pyridine in the vapor phase in the presence of catalysts.
At this time, various techniques have been developed for the preparation of 2-halopyridines such as 2-chloropyridine. One of these techniques consists more particularly in the preparation of 2-chloropyridine by a chlorination reaction of pyridine by means of molecular chlorine. This technique was the subject of developments of processes that can be divided into two large classes.
A first class comprises the socalled thermal processes, conducted in the vapor phase at high temperature, generally above 250xc2x0 C. and even 300 to 400xc2x0 C., and described primarily in U.S. Pat. Nos. 2,820,791 and 3,153,044 in the name of OLIN MATHIESON. These processes have various drawbacks such as a substantial formation of tars, causing the reactors or the ducts to clog up, and hence makes continuous execution of the process difficult. Furthermore these processes are accompanied according to the inventors, by high risks of explosion as well as corrosion.
A second class of processes comprises the processes initiated by means of light or ultraviolet radiation. Such processes have been described in particular in U.S. Pat. No. 3,297,556 in the name of OLIN MATHIESON and U.S. Pat. No. 4,054,499 in the name of SEITETSU KAGAKI Co. These processes, although they can be operated at lower temperatures than the socalled thermal processes, have the drawbacks of leading to the formation of tarry sub products that contaminate the light tubes and give rise to a subsequent diminution in the yield of the reaction. Furthermore these processes have to be operated in reactors permeable to the initiating radiation, that is to say more generally made of glass, which means that reactions embodied at high pressure are impracticable.
It is the object of the present invention to provide a new class of procedure for making 2-chloropyridine, and in general the 2-halo-pyridines without the drawbacks of the processes in the two classes described above.
The invention relates to a process for the preparation of 2-chloropyridine by a reaction of chlorination of pyridine by means of molecular chlorine, conducted in the vapor phase and with the intervention of catalysts, in which the catalysts utilized include at least one organic compound capable of generating free radicals under the conditions of the chlorination reaction.